I had a problem where in park it would show anything. I then found out the my reverse lights were not going on when I was in reverse. There is a sensor in the steering column, the portion the moves when you shift. I had to loosen up the retaining bolt on the bar next to the transmission and adjust it so everything is aligned properly.
I also think that if it is too far off the car sees it and makes changes. I may be wrong that this.